The Study Of Modeling And Simulation Methods For Bio-Soft Tissue

With the fast development of computer science and technology, medical simulation has progressed from only visual simulation into physical and physiology simulation. The basic problems is the bio-soft tissue modeling and simulation in the field of physics-based medical simulation with the representation of virtual surgery simulation. The main tasks include geometry modeling, physical modeling, deformation calculating, collision detection, interactive operations, visual feedback and force feedback. A survey of these key techniques and applications was presented in the paper and pointed out the studying focus is balancing the realism and real-time. This paper origins mainly from the project of National Science Fund on virtual eye simulation of Xiamen University, backgrounds on the surgery simulation of cataract and liver, also bases on the project of Fujian province fund which is the study for basic framework of virtual surgery simulation to integrate the related algorithms serving for future studying and application.The modeling and simulation for bio-soft tissue is a field in which multi-subject cooperate each other. The paper discussed the basic theory and methods about the bio-soft tissue modeling and simulation in 1) the data structure of geometry model, half-edge and half-face data structure; 2) the definition and methods about the mesh generation and subdivision; 3) the typical method of physical modeling; 4) the principle of medical image CT.Tearing capsule of lens is the first step of cataract surgery. The capsule of lens is a rich elastic thin and transparent tissue attaching on the lens. The paper discussed a whole procedure about the capsule in modeling and simulation. The outline of lens was rotated and discretized to get the surface model of triangles and is represented by half edge structure. The physical simulation model of the capsule was created by use of the linear elastic mass spring model with quasi static solving method, combined with the collision detection techniques. The paper implemented a progress cutting algorithm for the capsule cutting, also designed a tearing algorithms for capsule of lens in terms of the fracture mechanics principle. The paper simulated the capsule of lens not only in visualization but also in force feedback by using force feedback device to simulate the visco-stick friction and to make the simulation more realistic.Another important step of cataract surgery is breaking the kernel and aspirating it from eye. For this the paper investigated the tetrahedron dividing methods for virtual organ. It divided the cortex and lens into tetrahedron based on Delaunay rules and constrained with the triangle surface of lens capsule. Then an algorithm for breaking core of lens was presented based on half-face data structure. The process of emulsification and aspiration were simulated by means of the smooth particles hydrokinetics and the random deletion mechanism near the top of absorptiometer.It is a typical of medical simulation based on medical images such as CT image. It contains the image preprocessing and image segmentation, surface reconstruction using MC(marching cube) method, model simplification by QEM and smooth by Laplace operator and Finite Element Modeling. The paper discussed these contents in details and modified some methods such as the modeling of the liver organ, nasopharynx with multiply tissues and the optimization for QEM simplification. It also explored the simulation of visco-elastic soft tissue with FEM.The paper also presented an algorithm for surface model to simulate virtual organ in local adaptively. First we create a sparse mesh that can represents the organ in a allowable extent. Then we derived from it into a series level model by butterfly interpolate method. We integrated these levels model by a forest structure to implement dynamic subdividing simulation. This kind of method can enhance the precision of simulation in the case of not increasing the complexity of whole model. To lower computation complexity in the force/haptic feedback process a kind of collision detection method with hierarchical half-edge was presented. To make the simulation more faster, the paper discussed the basic principles and methods about GPGPU and the physical simulation by mass spring model and FEM on GPU.The paper analysed the importance and practical sense for creating a framework system of virtual surgery simulation and created the function and scene class diagram by system analysis and design. It found out the extendable key points and presented the hierarchical architecture of the framework. It provided a basic implementing strategy from some basic design patterns and the run mechanics of the surgery simulation system including two thread with a shared information synchronizer.In summary, the paper presented several methods such as adaptive dynamic local subdivision, collision detection by a hiberarchy-halfedge, GPU speeding methods and so on. Around the main line, the surgery simulation of cataract, the paper introduced the method of modeling and simulation about the lens capsule, cortex and kernel. The paper also disserted the modeling and simulation based on medical images systematically. At last, a basic software framework of surgery simulation was given. Still, the work what this paper has discussed is not enough. Author says he will study every part of the paper in future in more detail and more deeper.